Electron "Free Path" and Supra-Conductivity in Metals.

3 I have pointed out (Proc. Nat. Acad. Sci., 13, 43-46 (1927)) that the dual theory of electric conduction permits us to suppose the free to have the heat energy of gas molecules while the mean heat energy of all the conducting electrons may be much less. 4 In the first draft of his theory Sommerfeld, using, I believe, purely kinetic considerations, deduced Volta potential-differences which appeared to be of the right order of magnitude but were, unfortunately, of the wrong sign. Doctor Eckart now amends the theory by introducing something like the Volta conception of a specific attraction of different metals for electricity.